1. Field of the Invention
This invention relates to a method and an electric precipitation device for the production of semiconductor rods, and in particular to a method and apparatus for producing silicon rods. More specifically, the techniques of rod production include thermal disintegration of a gaseous compound containing the semiconductor material to be precipitated, precipitating the semiconductor material on at least one carrier member on a reaction chamber, which carrier member can be directly heated by means of an electric current which is made of the same material as that being precipitated, whereby the temperature of the thickening carrier member is controlled by adjusting the heating current flowing through the cross section of the carrier member.
2. Description of the Prior Art
A somewhat similar method to that disclosed herein is known from the Austrian Letters Patent 222,184 wherein an image is produced of the glowing semiconductor carrier member by means of an optical system, of the diameter of the image which changes with the diameter of the growing rod during the precipitation process is scanned with the help of a movable photocell and the bright-dark contrast which occurs in the picture plane at the limit of the light beam which emerges from the semiconductor rod is utilized for controlling a device which moves the photocell away from the focused beam and simultaneously increases the current in the heating circuit to such a degree that the temperature of the semiconductor rod is maintained at a desired, in particular constant, value.
From the German Offenlegungsschrift 1,444,421, another method for the operation of an electric precipitation device for obtaining pure semiconductor materials, such as germanium or silicon by means of thermal disintegration and precipitation on corresponding carrier members from compounds containing these elements is known. It is disclosed that the glowing temperature of the carrier or precipitation members which are heated to the dissociation temperature of the semiconductive compound is sensed with the help of a pyrometer in such a way that the radiation intensity of the radiation emitted by the precipitation member and growing with its cross sectional growth is transmitted onto the radiation sensitive surface of the pyrometer. Thereby, a surface is radiated onto the pyrometer, which surface grows in accordance with the growth of the cross section of the rod, whereby the growth of the radiating surface and the electric value produced thereby at the pyrometer with its changing absolute values are used to control or regulate the precipitation device when the growth reaches predetermined marginal values or interruption in the steady growth of the surface is encountered.